S3172 Pseudomelanosis Coli: A Historical Review and Explanation for Increased Incidence in the Western World

Abstract

INTRODUCTION: Pseudomelanosis coli is the brown-black pigmentation of colon and rectum as a consequence of laxative use secondary to increasing dependency on narcotics. However, there are reports of Pseudomelanosis in the absence of laxatives and pigmentation in areas other than colon. Recently it has also been linked to colon cancer. METHODS: A selective review of existing literature on Psuedomelanosis coli was performed in PubMed. RESULTS: Early studies speculated that the pigment is melanin or an anthracene derivative. Now it is widely accepted that the pigment is actually lipofuscin. Lipofuscin predominantly accumulates in the macrophages of the lamina propria, usually in the colon. Electron microscopic examination of the pigment granules in the duodenum has revealed lysosomal bodies containing iron sulfide with traces of minerals from antacids, food additives and dental fillings. Electron microscopy of ileum revealed the pigment granule laden macrophages containing predominantly magnesium and aluminum-rich silicates. Pseudomelanosis is characteristically absent in colonic neoplasms. The area of the melanotic colon with cancer association has reduced or even lack of pigment laden macrophages. Pseudomelanosis is sometimes encountered in colonoscopy without a history of laxative use. This means that either chronic inflammation or a rapid intestinal transit in inflammation can cause pigmentation. Based on studies in guinea pigs, it is hypothesized that non-anthraquinone laxatives have the potential to cause microscopic pigment deposition, which may not result in gross discoloration on endoscopic evaluation. CONCLUSION: Pseudomelanosis coli has increased in incidence in the United States due to increasing incidence of chronic pain syndromes causing opioid dependence and secondary laxative use and with abundant purine intake. Non-anthracene Pseudomelanosis coli has a different pathogenesis and may be missed by endoscopists due to the grossly normal appearing colon. The pathogenesis of Pseudomelanosis coli in the setting of laxative naïve patients is not well understood. Interestingly, chronic colitis may have an association with Pseudomelanosis coli. There is no established correlation between Pseudomelanosis coli and cancer, but it is unclear if chronic colitis causing Pseudomelanosis has any role in carcinogenesis in these patients. Lastly, melanosis can occur in other parts of the gastrointestinal system, but is usually due to other pigments rather than lipofuscin. Further studies are needed.